Arsenic stabilization of calcium arsenate waste by hydrothermal precipitation of arsenical natroalunite

作者：Vinals J^*; Sunyer A; Molera P; Cruells M; Llorca N

来源：Hydrometallurgy, 2010, 104(2): 247-259.

DOI：10.1016/j.hydromet.2010.06.013

• Arsenic
• Stabilization
• Sodium alunite
• Gypsum
• Copper smelter waste

The stabilisation of calcium arsenate waste from a copper smelter by precipitation of arsenical natroalunite has been investigated. This procedure could solve the problem of arsenical gypsum production because it is transformed into arsenic-free anhydrite. Natroalunite precipitation was studied at 180-200 degrees C from the slurry obtained after H(2)SO(4)-leaching and zonation of the original waste - using sodium and aluminum sulfates as reagents. Calcium arsenate waste and final precipitates were characterized by chemical analysis (ICP), SEM-EDS and XRD. Solubility tests were also performed on original waste and selected precipitates.
The effects studied in the hydrothermal treatment were: initial pH, Al/As molar ratio, As concentration, reaction time and prior gypsum removal. For (Al/As)(aq) = 4.5, a complex natroalunite (-(Na,Ca)(Al,Fe)(3)((S,As,P)O(4))(2) (OH)(6))) was extensively formed. Under these conditions, As-substitution in TO(4) was 7-8% molar. Decreasing (Al/As),, increased As-substitution in natroalunite (up to similar to 14% molar) but mansfieldite ((Al,Fe)(As,P)O(4)center dot 2H(2)O) co-precipitated. Other effects such as the arsenic concentration in the range 3.5-7.0 g/L and prior gypsum removal did not significantly alter the arsenic phase ratio and the composition of the arsenic phases. However, treatment at 180 C increased mansfieldite precipitation. Calcium incorporation in natroalunite was small (similar to 0.04 in formula) and for initial pH = 1, precipitation of Cu, Ni and Zn was insignificant.
Arsenical natroalunite can be effective for long-term storage. At its natural pH (4-5). arsenic solubility remained stabilized at similar to 0.1 mg/L in 6 months. Mansfieldite was not stable under the same conditions with arsenic solubility between 5-10 mg/L The major disadvantage of natroalunite is the limited arsenic partition between solid and aqueous phases (similar to 0.45 molar). However, as the precipitation rate is fast (<15 min), it seems technically feasible to improve the arsenic precipitation yield by semi-continuous addition of reagents in a single hydrothermal operation. Cadmium incorporated into the anhydrite structure causes cadmium release in leachates. It seems that this problem can only be overcome through prior removal of cadmium from the plant effluent.

• 出版日期2010-9